Despite the importance of the effect of aging on productivity and quality of life, little is known descriptively about individual differences in aging. Next to nothin is known about the etiology of these phenomena. It is generally agreed that he most powerful strategy to untangle genetic and environmental influences in the development of human characters is the adoption design, and that the most powerful adoption design is the study of twins reared apart. An unprecendented opportunity for the study of an elderly population has arisen in Sweden where a sample of 300 pairs of elderly twins who were reared apart has been identified in the Swedish Twin Registers. During the proposed 5-year program project, we will administer a 2-day battery of behavioral and biomedical measures to this unique sample of twins and to a sample of matched controls from the Swedish Twin Registry. The behavioral program will include measures of specific cognitive abilities, general intelligence, personality, information processing, psychopathology, attitudes, general intelligence, personality, information processing, psychopathology, attitudes, and interests. The biomedical program will include a medical examination, detailed health history (including mutrition and drug use), blood pressure, and blood urine analyses. This interdisciplinary approach will have synergistic benefits in advancing our understanding of individual differences among the aged as well as in the aging process. Twins 65 years of age and older will be tested every 2 years, and twins up to 65 will be tested every 5 years. The proposed project will be the first step in a continuing longitudinal study to assess the genetic and environmental etiology of individual differences among the elderly and in behavioral and biomedical aging.